1. Field of the Invention
The invention concerns a device for facilitating the ventral screwing together of dens fractures with compression screws, characterized by a guide tube assembly comprised of two guide tube casings which are pivotably joined near one end by means of an articulated joint, and which are adjustable within a predetermined range of angles by an adjusting means. Bore wires, milling tools and compression screws can be introduced into the dens via the guide tube assembly at precise spatial and angular relationships set by the aiming tube assembly.
2. Description of the Related Art
Breaks in the dens, finger like projection of the second cervical vertebra, occur relatively frequently as a result of accidents involving the neck vertebrae. Processes have been devised for gaining frontal operational access to the cervical vertebrae for inserting screws to connect the fractured sections with each other. This type of process is often described in the literature, as for example the process according to Bohler, J. "Schraubenosteosynthese von Frakturen des Dens" (Screw Osteosynethesis of Fractures of the Dens) Unfallheilkunde (Injury Treatment Science) 84 (1981), pages 221-223 or a process according to Knoringer, P. "Zur Behaldlung frischer Frakturen des Dens axis durch Compressionschraubenosteosynthese" (Concerning the Treatment of Fresh Fractures of the Dens by Means of Compression Screw Osteosynthesis) Neurochirurgia 27 (1984), pages 68-72. The above described processes have been widely studied and have found acceptance in clinical practice.
When using the above mentioned surgical processes it is necessary to prepare a relatively large access opening from the front. Trachea as well as esophagus, as well as carotid arteries and jugular veins, are pushed out of the way and the neck soft parts are held aside by means of hooks. Guided by the aid of radiation imaging, boring wires (so-called churchmans wires) with a cross section of 0.5 mm are screwed into the neck vertebrae and the dens tip. Thereafter a milling cutter is slid coaxially over the boring wire and up to the entry point of the cervical vertebra. The milling cutter is used to create an insertion starting point at the entry point for a self cutting dens hollow screw. The dens hollow screw is slid over the bore wire after removal of the milling cutter and screwed into the cervical vertebrae. The dens hollow screw is constructed as a so-called compression screw, that is, it is provided with two different segments having different threads, so that upon the screwing in of the screw the two fragments are caused to be pulled towards each other and are finally held tightly pressed against each other. Hereby the two bone pieces are held in place.
For an optimal fixing of the two fragments it is necessary to implant two screws. The significance of the second screw is that it prevents the rotation of the two bone pieces with respect to each other. Only so is a connection of bones to be securely established. The implanting of the second screw, however, frequently is problematic, since the dens is relatively thin and therefore provides a severely limited working space. If the first screw is not properly placed, the insertion of a second screw is frequently precluded.